EXAM II Study Flashcards
What is the main purpose of a telescope
To collect as much light as possible in the shortest time and resolve small details
What determines a telescope’s efficiency
The area of the mirror or lens
Why are the large mirrors preferred over lenses for telescopes
they are cheaper, easier to maintain, and suffer less from absorption and refraction
what are the main uses of telescopes
imaging, spectroscopic studies, and long term monitoring
what limits ground-based telescopes
atmospheric distortion, which can be improved by adaptive optics and interferometry
what are the three main types of spectra
continuous, discrete, and absorption
continuous spectra
When light emitted from a solid substance passes through a prism, it produces a continuous spectrum of colors
emission spectra
a spectrum of the electromagnetic radiation emitted by a source.
absorption spectra
A combination of emission and continuous spectra
what kinds of material produces a continuous spectrum
hot, dense materials like solids. Spectral lines are unique to the element that produced them, making them identifiers of elements which can be used to identify elements in the composition of distant astrophysical objects
what produces an absorption spectrum
a cold gas in front of a hot source, absorbing specific wavelengths. the dark lines are emission lines that have been absorbed. These emission lines correspond to energy levels in atoms.
how are spectral lines used in astronomy
to identify elements and determine velocity and direction via the Doppler effect
what are the main components of the sun
hydrogen and helium
what percentage of the sun is hydrogen
more than 70%
what percentage of the sun is helium
more than 20%
What are the three main layers of the sun
core, radiative zone, and convective zone
How does energy move within the sun?
photon diffusion in the radiative zone, conviction in the convective zone
what is the solar wind?
a stream of charged particles escaping the sun
How is the sun’s magnetic field generated
by differential rotation of plasma layers
what defines a star?
an object that produces energy via nuclear fusion
what are the two main types of planets
jovian and terrestrial
what differentiates dwarf planets from other planets
they are small, icy/rocky, and do not clear the orbits
what are asteroids
irregularly shaped rocky/metallic objects mostly found in the asteroid belt
what are the primary characteristics of jovian planets
large, gas-rich, possesses rings, and many moons, strong magnetic fields
why is venus the hottest planet
its dense CO2 atmosphere creates a strong greenhouse effect
what evidence suggests mars once had liquid water?
surface features indicating past water flow
what is unique about uranus and venus’ rotation?
they rotate in a different direction than other planets
what is the great red spot on jupiter
a massive storm that has lasted for centuries
why does jupiter emit more energy than it recieves?
due to gravitational contraction and internal heating
what is gravitational contraction
the process in which gravity causes an object to contract, thereby converting gravitational potential energy into thermal energy
doppler effect
An observed change in the frequency of a wave when the source or observer is moving
What is the surface temperature of the sun
5700 degrees K
How hot is the core temperature of the sun
15 million degrees Celsius (27 million degrees Fahrenheit), hot enough to sustain nuclear fusion
How long does the journey take for the energy from the core to reach the sun’s surface
100,000 years
What are the two forces that keep the sun in a constant state of equilibrium
gravitation and radiation pressure
The Sun converts hydrogen to helium in its ______.
core, via nuclear fusion
What is the prime reaction in the proton-proton chain where nuclear fusion occurs
4 protons are converted to helium, energy, positrons, and neutrinos
High temperature is needed in the sun to overcome what?
core, repulsive electromagnetic force due to positive, proton-proton, nuclei
Why is the very high density in the core needed
to accommodate interactions between protons
Nuclear reactions in the core generate vast amounts of ___ which is transported through the ___ zone via ____
energy, radiative zone, photon difussion
what is proton difussion
scattering and absorption
How is energy transported in the convective zone
via physical motion of hydrogen gas/plasma
Outer layers of the sun include a ___ which we see as a surface
photosphere
how deep is the photosphere
thin, a few hundred kms
what is the corona
a wispy layer of the sun approximately 1 million degrees and is only seen when the central disk of the sun is blocked
why is the corona very hot
energetic electrons moving under the action of magnetic field
what is the solar wind comprised of
energetic electrons, protons, and helium ions which escape the surface and travel outwards, interacting with objects in the solar system
How do we know the structure of the interior of the sun?
modeling motion of gas/plasma using the laws of physics and via measuring properties of escaped particles such as neutrinos, electrons, positrons, protons, helium ions etc.
How do we know the temperature of the surface of the Sun?
measuring the continuous spectrum of the sun
How do we know the constituents of the Sun
by analyzing the spectral lines, hydrogen and helium emission lines
the sun has a magnetic field, how is it generated ?
via the differential rotation of gasses/plasma layers that include moving charges
What is nuclear fusion, in terms of the star
the proton-proton chain that produces He and energy, which is the simplest reaction
at what temperature does the p-p chain of He and energy occur
between 10 and 15 million degrees kelvin
at what rate does the sun rotate about its axis?
1 revolution per 27 days
how hot is the sun’s surface temperature
around 6,000 degrees K
what is the sun’s magnetic field comprised of
a Hydrogen and Helium mixture where Hydrogen dominates at around 70%
What are the characteristics of our solar system’s behavior
all planets revolve around the sun in the same direction and in a similar plane. all planets rotate about their own axis
What shape are the majority of the orbits in the solar system
elliptical
What are characteristics of mercury
- extreme variation between day/night temperatures
- no atmosphere
- small magnetic field
- heavily cratered, likely due to collisions during its formation
What are characteristics of venus
- hottest planet because of greenhouse effect
What are characteristics of Mars
- light atmosphere of CO2
- possesses a magnetic field
- surface features indicate flow of water
- has 2 irregular shaped moons, probably captured asteroids
What is the most dominant jovian planet?
Jupiter
What is Jupiter comprised of
Hydrogen and Helium, though not massive enough to produce nuclear fusion
Why does jupiter produce a large magnetic field
electrical charges moving in the interior as well as a differential rotation of the surface layers. At the deepest layer, hydrogen behaves like a liquid metal
We know how fast a distant galaxy is moving away from us on the basis of its
spectrum, doppler effect
According to the laws of thermal radiation, hotter objects emit photons with
a shorter average wavelength
Suppose you know the frequency of a photon and the speed of light. What else can you determine about the photon?
its wavelength and energy
We can see the Moon because it
reflects visible light
You observe a distant galaxy. You find that a spectral line of hydrogen that is shifted from its normal location in the visible part of the spectrum into the infrared part of the spectrum. What can you conclude?
the galaxy is moving away from you
Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
The cloud is cool and lies between you and a hot star
From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?
gamma rays, x-rays, ultraviolet, visible light, infrared, radio
Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?
the wavelengths of spectral lines in the star’s spectrum
Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star’s spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude?
The star is moving toward us.
Thermal radiation is defined as
radiation with a spectrum whose shape depends only on the temperature of the emitting object.
Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude?
Star X is moving away from us faster than Star Y
Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color?
Its surface is cooler than the surface of the Sun.
Which of the following stars is the hottest? Red star, yellow star, blue star, green star
blue star
What observational techniques is most appropriate for measuring Doppler shifts?
spectroscopy
Suppose that two stars are identical in every way; for example, same distance, same mass, same temperature, same chemical composition, and same speed relative to Earth, except that one star rotates faster than the other. Spectroscopically, how could you tell the stars apart?
The faster rotating star has wider spectral lines than the slower rotating star.
When an atom’s electrons fall down to lower energy levels in a thin cloud of hot gas, what is produced?
an emission line spectrum
We know the Sun is primarily made from hydrogen and helium on the basis of its
spectrum
The Chandra X-ray Observatory must operate in space because
x-rays do not penetrate Earth’s atmosphere
Which of the following observational techniques is most appropriate for measuring Doppler shifts?
spectroscopy
What telescope is best suited for studying the hottest intergalactic gas (10 million K) in a cluster of galaxies?
Chandra X-ray Telescope
Why can’t x-ray and gamma-ray telescopes use the same designs as visible-light telescopes?
X-rays and gamma rays have so much energy that they cannot be reflected in the same way as visible light.
What is the purpose of interferometry?
It allows two or more small telescopes to achieve the angular resolution of a much larger telescope.
What does angular resolution measure?
the angular size of the smallest features that the telescope can see
What is the purpose of adaptive optics?
It reduces blurring caused by atmospheric turbulence for telescopes on the ground.
The stars in our sky twinkle in brightness and color because of
turbulence in the Earth’s atmosphere.
Which of the following wavelength regions can be studied with telescopes on the ground?
radio, visible, and very limited portions of the infrared and ultraviolet regions
The light-collecting area of an 8-meter telescope is ________ times that of a 2-meter telescope.
16
Which of the following best describes why radio telescopes are generally much larger in size than telescopes designed to collect visible light?
Getting an image of the same angular resolution requires a much larger telescope for radio waves than for visible light.
Which of the following statements best describes the difference between a refracting telescope and a reflecting telescope?
A refracting telescope uses a transparent glass lens to focus light, whereas a reflecting telescope uses a mirror to focus light.
Suppose you want to determine the chemical composition of a distant planet or star. Which of the following will be most useful to have?
high spectral resolution
